1. Field of the Invention
This invention relates to a means for preventing the backflow of fluid, such as water, from a downstream outlet to an upstream supply, and more particularly, to a backflow valve designed to prevent the flow of carbonated water from soft drink dispensers into the fresh water supply systems for the soft drink dispensers, and to indicate that a backflow condition has occurred, or currently exists in the system.
2. Discussion of the Prior Art
Beverage postmix carbonators have been known to leak carbon dioxide, CO.sub.2, back into the fresh water supply lines that feed the dispenser. The presence of carbon dioxide can acidify the water in supply lines, and if the supply lines are made of copper, the acid will leach copper or copper compounds into the water supply. When the carbonator recycles, some of the contaminated water can be drawn into the beverage dispensing system. The result, depending on the concentration of copper in the water and other conditions, will result in an off-taste and in extremely high concentrations, nausea and vomiting of those who consume the contaminated beverage. In addition, the contaminated water can also be drawn into other beverage dispensers operating from the same water supply or can be consumed through drinking fountains utilizing the same water supply.
The adverse health effects of drinking water or carbonated water which contains copper are fleeting, even in the highest concentrations which result in nausea and vomiting. The effect of copper ingestion on an individual should last at most a few hours, and there are no known instances of death or ongoing distress. Copper and its compounds are often found in water and are not considered toxic, but rather, they are considered irritants.
One known cause for CO.sub.2 backflow into fresh water or potable liquid supply lines is a sudden pressure drop in the main supply line, coupled with the failure of the check valves at the water inlet of the carbonator. For this reason, double check valves are normally specified for potable water applications. Failure events in a double check valve occur only very infrequently, and thus far, a failure condition in the valves has been impossible to duplicate in the laboratory or in the field. On rare occasions, however, examination of a failed double check valve show that the conventional strainers or filters utilized in the valve assembly have failed allowing particles to enter and lodge in the check valve. The lodged particles can therefore hold the check valve open, which results in a backflow condition.
Although there is a tendency to blame copper contamination on the failure of the check valves, there are a variety of other conditions that exist that can cause the contamination problem. One such condition is that of the excessive use of solder flux when assembling the copper piping utilized in the system. The excess use of solder flux can result in localized acidity in the copper line thereby resulting in the same leaching condition as caused by carbonation backflow. A second condition that can cause the contamination problem is the use of naturally acidic water, that is, water with a pH less than 7. Depending on the degree of acidity, such water can leach copper directly from copper pipes, even when no carbon dioxide is present. There are some water supplies which can have acid conditions which can range to unusually low pH values. New York City water, for example, has ranged as low as a pH level of 5, which is 100 times more acid than neutral. A related problem to low pH water is soft water. In a soft water condition, the addition of chlorine can result in wild fluctuations in acidity, and as stated previously, such conditions can result in contamination problems from direct leaching. A third cause of the problem can be excessive chlorination. Some municipalities, Washington D.C. for example, demand that new plumbing, including replacement parts, be chlorinated for twenty-four hours before use after installation is complete. This excessive chlorination procedure can also lead to acidic water conditions and resultant copper leaching.
Although there are other possible causes of copper contamination as discussed above, the carbonation backflow cause is one that can be prevented locally. There are several techniques employed to prevent carbonation backflow in soft drink dispensers or post mix carbonators. One such technique is the indirect fill method. In the indirect fill method, which is used on all post mix cup vendors, water is drawn from a reservoir to supply the carbonator. The reservoir is filled with water through a solenoid valve that is controlled by the level of water in the reservoir. Although preventing carbonation backflow, this system provides an opportunity for microbiological build-up if regular maintenance and cleaning of the reservoir are neglected. For this reason, vending operators need regular and frequent sanitizing of the water systems in postmix cup vendors in spite of the relatively protected environment within the vendors. To use an indirect water supply for conventional postmix systems would lead to almost impossible sanitizing tasks because of the environmental conditions in the average dispensing location.
A second technique makes use of solenoid valves in addition to check valves at the inlet to carbonators. The use of solenoid valves prevents carbonator backflow, however, as in the indirect fill method, this technique can lead to microbiological contamination or water leak back. The problem arises because the solenoid valve needs a few milliseconds to close, and it is during this time period that the leak back occurs.
A third technique makes use of vented check valves. Vented check valves are devices which are intended to open if back-pressure, becomes higher than line pressure for any reason. There are several varieties of these vented valves using diaphragms, flexible seals or pistons designed to produce an opening-to-atmosphere effect. All of the vented devices depend on the reliability of a check valve to operate and thus vented check valves are no more reliable than conventional double ball check valves. In addition, because of their design, they are less self-cleaning than conventional check valves because the velocity of water passing through them is much slower.
In the patent art, there are a variety of backflow preventers for regulating the reverse flow of liquid, although not necessarily in beverage dispensing machines. In U.S Pat. No. 4,646,775, Traylor discloses a vacuum breaker for connection in the discharge line of a source of liquid. This patent also discloses an upstream backflow preventer. The backflow preventer comprises a central nozzle portion made out of a resilient material and which is mounted in the discharge line. The nozzle portion of the backflow preventer diminishes in cross-section in a downstream direction. Under normal operating conditions, a flow of liquid under pressure enters the backflow preventer and forces the nozzle open. If there is a pressure build-up on the downstream side of the nozzle, then the downstream extremity of the nozzle closes and prevents water flow in the upstream direction.
In U.S. Pat. No. 3,417,775, Smith discloses a vacuum breaker device having a backflow preventer incorporated therein for preventing the backflow of fluid therethrough. The backflow preventer comprises a diverging type nozzle made of a resilient type material. When the pressure upstream is greater than the pressure downstream, normal operating conditions, the nozzle is substantially open and fluid flows through easily. However, when the pressure downstream is greater than the pressure upstream, the nozzle portion expands and seals off the water flow paths.
In U.S. Pat. No. 3,122,156, Kersch discloses a flexible check valve/anti-siphon device. The check valve controls the reverse flow of a fluid, whether it be a liquid or gas, in a particular flow line. The check valve is conically shaped and made of resilient material. Under normal operating conditions, the fluid pressure upstream of the check valve forces the valve to open and fluid readily flows therethrough. When the pressure downstream of the valve builds to a point where it is greater than the pressure upstream, the check valve moves or deflects thereby forcing the peripheral edge of the conical portion radially outward against the inside surface of the flow line thus sealing off the line.